what places enlarge photos "movie poster" size

have you seen those posters at the theater of upcoming movies?
what places enlarge photos that size?
because i have a project for school and one of the criteria for our movie project was to make a poster of it. i don't want to have to waste my own ink and make it all sloppy. so what places? i have never really done this before so i don't know where to start. i don't want to do it online, because i need it as soon as possible.

wait walmart does it?
how much and how long does it take?
also does the photo they are going to work off have to be a certain size? cause mine is about 8 1/2 X11 if you eclude the white boarders cause the printer cant reach that far.

her in so-cal we have a store called CVS (was sav-on drugs) and i checked online and it says they do 20' x30' in for $20 bucks and its gloss too.
the only reason i cant go there is because you have to do it online and they dont do it instore so you will have to wait a while. but i need it ASAP.

one thing to mention....once i took in a picture on a card that i wanted to enlarge to kinkos...but they refused to enlarge it b/c it is technically copyrighted material. if you are planning on blowing up a photo from a movie, you may meet resistance.

I have had walmart refuse to make prints because they were by a professional (me?? thank you). I had to go fill out and sign a release showing that I owned the the rights to the pictures I took
Related to that, if you hire a photographer, you should get uncompressed digital copies if they use a digital camera. Make sure you get a release also. This will cost you more but you will probably come out better later on, esp if you want prints years down the road (you will not have to rely on copies).